The present invention relates to a noise analyzing apparatus for analyzing noise of an autonomous system consisting of electronic circuits such as an oscillator a multi-vibrator, etc.
As a method for analyzing noise of an electronic circuit, there is a method for adding a noise source to a linear equivalent circuit at a DC operating point and calculating a transfer function from the noise source to an output, thereby to calculate output noise. However, this method can not be applied for analyzing noise of such a system like an oscillator of which the operating point changes according to a lapse of time.
On the other hand, in the following literatures 1! and 2!, there have been proposed methods for analyzing noise of such circuits like a mixer circuit and a switched capacitor circuit of which operating point changes periodically when a periodical excitation is added to these circuits.
Literature 1!: Makiko Okumura, Hiroshi Tanimoto and Tsutomu Sugawara, "Noise analysis by computer for nonlinear circuits having two input signals", the Institute of Electronics, Information and Communication Engineers, Papers A, Vol. J73-A No. 8, pp. 1342-1349, 1990.
Literature 2!: Makiko Okumura, Hiroshi Tanimoto, Tetsuro Itakura and Tsutomu Sugawara, "Numerical noise analysis for nonlinear circuits with a periodic large signal excitation including cyclostationary noise sources", IEEE Trans. Circuits Syst., I: Fundamental Theory and Applications, Vol. 40, No. 9, pp. 581-590, September, 1993.
However, none of the above-mentioned literatures describe a method for analyzing an autonomous system of which the operating point changes periodically. Accordingly, there has so far been no method for simulating noise of a general autonomous system prior to a trial manufacturing of the system, and there has been no way but making a rough estimate of noise from the past experience at the stage of designing.
Further, the following literature 3! discloses an apparatus for calculating noise of an oscillator.
Literature 3!: Andy Howard, "Simulate oscillator phase noise", Microwaves & RF, pp. 64-70, November, 1993.
However, according the method in the literature 3!, it is possible to calculate only noise of an oscillator including a resonator and it is not possible to calculate noise and output a result of analysis by splitting the output power into amplitude noise and phase noise.
With a view to eliminating the above-described problems, it is an object of the present invention to provide a noise analyzing apparatus which can analyze noise of an autonomous system by simulation prior to the manufacturing of the system, without actually involving a trial manufacturing of the system.
Further, it is another object of the present invention to provide a noise analyzing apparatus which can calculate noise by splitting output power into phase noise and amplitude noise and output each noise for improved precision of the output of each noise.